Japanese Patent Unexamined Publication No. 2004-7332 discloses a speaker shown in FIG. 3 in which voice coil unit 2 that is movably disposed on magnetic circuit 1 is coupled to the inner peripheral end of diaphragm 3 and the outer peripheral end of diaphragm 3 is coupled to frame 5 via edge 4. In this speaker, the rear surface of diaphragm 3 is coupled to frame 5 via suspension holder 6 and edge 7. Furthermore, edges 4 and 7 are allowed to protrude in the opposite directions to each other, thereby allowing the vertical amplitude to be vertically symmetric. Thus, the distortion of the speaker is reduced.
However, when such a speaker structure is employed, suspension holder 6 is formed so as to have at least the same level of rigidity as that of diaphragm 3. This causes the driving load of magnetic circuit 1 to increase. As a result, it is difficult to improve the driving efficiency of a speaker.